To further aid proper ADHD diagnosis, all potential participants will be administered a battery of neuropsychological tests. Potential ADHD participants will undergo testing while unmedicated. This battery will include IQ, and attention and memory tests (WASI, Trail Making, Symbol Digit, Stroop Test, and Rey AVLT), as well as several measures of executive functioning known to be sensitive to the cognitive deficits observed in ADHD samples (Kaplan & Stevens, 2002). Normal performance on all cognitive tests known to be sensitive to ADHD will exclude participants from the study. Full Scale IQ score from the WASI below 80 or above 120 will exclude participants from further participation. Diagnostic interviews using the SCID-IV (First et al., 1996) will be used to obtain a detailed psychiatric history. Lifetime or current history of other major Axis I psychiatric disorders, including bipolar disorder, schizophrenia, substance dependence disorders, or obsessive-compulsive disorders, will exclude potential participants. These disorders may better explain the presence of attention symptomatology, which DSM-IV criteria indicate precludes an ADHD diagnosis. In addition, the disruptive behavior disorders module of the K-SADS-PL will be used to evaluate the presence of childhood Conduct Disorder and adult Antisocial Personality Disorder (ASPD). These diagnoses will also exclude further participation, as these conditions may be better associated with different abnormalities in prefrontal brain function (Bauer, 1997; Stevens et al., 2001). Potential participants also will be excluded if they report a history of head injury (e.g., loss of consciousness > 10 min), seizure disorder, life threatening disease, family history of schizophrenia, uncorrected visual or auditory deficits, or conditions contraindicated for MRI (claustrophobia, metal in body, pregnancy, etc.). Up to 25% of persons with ADHD suffer from learning disorders (Tannock & Brown, 2000). Because educational failure is so prevalent in this group, we will include these people into the study. While the strict inclusion criteria will exclude many potential participants, this is necessary to ensure a homogenous participant population that varies by the presence or absence of ADHD.